Build a hanging dipole for two metres
Described here is a simple omnidirectional, vertically-polarised
dipole for two metres. Made from coaxial cable, it can be rolled
up and stored in a small container. It may be used as is indoors,
or waterproofed for use outside. No extravagant gain claims are
made; this dipole has no more gain than any other. However, it
should be significantly more effective than the antenna that came
with your handheld. The cost of building the project is around
five to ten dollars. Allow about 20 minutes to construct and erect
the antenna.
A single length of 50 ohm coaxial cable forms both the antenna
element and the feedline. The antenna is made by removing a quarter
wavelength of outer jacket and bending the braid back along the
cable towards the transceiver to form a vertical dipole. This
means no metal work or wiring is required (apart from attaching
the BNC or PL259 plug).
Parts required
The following is required to complete the project:-
- 3-4m RG58 coaxial cable (not critical - use longer length
if height is needed or the operating position is distant from
the antenna)
- PL259 or BNC plug (to suit transceiver)
- small metal lug, washer or nut
- tape measure, scissors, small screwdriver, long-nosed pliers,
multimeter, fishing line, soldering iron
Construction
- Solder the PL259 or BNC plug to one end of the RG58 cable.
- From the other end of the cable remove 48 cm of the black
plastic outer covering to expose the braid.
- With a small screwdriver (Phillips head is best) gently part
the braid to make a small hole near where it ceases to be covered
by the plastic jacket. Aim to make it about 5mm in diameter.
- Use either pliers or a screwdriver to pull the inner conductor
out from inside the braid through the hole in the braid (Fig 2c).
- Fold the braid back along the cable towards the plug. Solder
the end of the braid to prevent fraying.
- Remove about 5mm insulation from the inner conductor.
- Solder the end of the inner conductor to a small metal lug
or nut.
- Thread fishing line through the lug or nut and hang the antenna
in its desired position.
The antenna is now operational. You may wish to check the SWR
and make it longer or shorter if the SWR is above about 1.5:1
at 147 MHz (or 145 MHz in Europe or other areas where 2m is 144 - 146 MHz).
Erection and use
The antenna should be hung vertically for best performance. Keep
it away from metal objects and have it as high as possible. Where
signals are weak, hang the antenna near a window facing the repeater.
If you intend to use the antenna outside, apply sealing compound
to stop moisture entering the cable. Not doing this will mean
poorer performance over time as cable losses increase.
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